Bitdepth for DAC

I have recently got a new DAC : Musiland MD-10. It uses CS4398 D/A chip and offers a special function of Bitdepth at 16, 20 and 24 bits selectable. The manual does not mention in what circumstances or what types of CD to be played, should a 16, 20 or 24 bits depth be selected for best performance. Could any experts out there tell me what does this function work for and how to make this bitdepth function work best? Here is the link for the DAC that I have got.

Eddie, I think the selector is meant to match your player's rate. No harm in trying each level with any player though. This unit may upsample via the selector, whereas some will do so automatically, like my Classe unit. The manual selection might be a useful feature.